Bar Chart

A bar chart or bar graph is a chart that represents categorical data with rectangular bars with heights proportional to the values that they represent. Here one axis of the chart plots categories and the other axis represents the value scale. The bars are of equal width which allows for instant comparison of data.

Quick details

What: Discover Proportion, Rank

Why: Make decisions on qualitative data through simplistic visual comparisons

History of Bar Chart

Nicole Oresme, used a bar chart in the 14th century, in his publication titled – The Latitude of Forms where he plotted the velocity of a constantly accelerating object against time for the first time. Another visual representation of a bar chart came into the picture in 1765 when Joseph Priestley used individual horizontal bars to visualize the lifespan of a person and the whole chart to compare the life spans of multiple persons.  However many sources still consider William Playfair to have invented the bar chart, where he represented the Exports and Imports of Scotland to and from different parts for one year published in The Commercial and Political Atlas which makes it known to be the first bar chart in history.

Nicole Oresme’s  chart The Latitude of Forms b) Exports and Imports of Scotland to and from different parts for one Year from Christmas 1780 to Christmas 1781 c) A Chart of Biography to serve as visual study for Joseph Priestly’s Lectures on History and General Policy

 

When to Use a Bar Chart

1When you need to compare a large set of categorical values

Use bar graphs/charts to represent comparisons among discrete categories visually when categories are qualitative. Such categorical data is a grouping of data into discrete groups, such as the months of the year, age group, shoe sizes, and animals. Also use bar charts as an alternative to column charts for showing a larger set of data, where the vertical alignment of labels give more space for text to be easily read for each category. Technical analysts use bar charts – or other chart types like candlesticks or line charts – to monitor the price performance of assets which aids in making trading decisions.

A bar chart comparing the wind energy production in different states of USA

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2When required to compare multiple categories or sub-categories simultaneously

Use bar charts when comparison is required for both categories and subcategories, using bars clustered in groups of more than one, showing the values of more than one measured variable. 100% Stacked bar charts work really well here to indicate how much each sub-group contributed to its category’s total. It can be used to compare how entities are performing against each other and how much did each of the sub-groups contribute to the whole.

Stacked bar chart comparing consumer spending across different categories for different generations

3When you need to  visualize two data sets on a single chart

Use overlapping bar charts to allow comparison of similar data sets using differential width bars on the same chart. It can serve a dual purpose where on one axis, bars compare categories, while on the other they represent a discrete value. Also preferentially selecting or deselecting legend labels, a single data set can be viewed or a comparison of two data sets can be done simultaneously.

Overlapping bar chart comparing branch efficiency across locations in terms of people and profits

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4When you need to gather insights on deviations in data

Use column charts(vertical bar charts) when required to compare values that tend to go into negatives as well as positives. Alternatively, these charts can also be used to compare performance against an average benchmark or do a deviation analysis.

Column chart comparing net migration for different countries

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Types of Bar Charts

1. Pareto charts

These charts are arranged from highest to lowest incidence.

2. Column or Vertical Bar Charts

The categories appear along the horizontal axis; the height of the bar corresponds to the value of each category. These charts are excellent for mapping data sets over a period of time.

3. Stacked Bar Chart

Stacked bars that represent different groups on top of each other. The height of the resulting bar shows the combined result of the groups.

4. Grouped Bar Chart

For each categorical group, there are two or more bars which are color-coded to represent a particular grouping.

 

When Not to Use a Bar Chart

1When you need to represent and compare a continuous set of data

Do not use Bar Graphs when you need to represent continuous ordered quantities. In case of continuous data (such as a person’s height) needs to be represented then use a Histogram. It is a best practice to leave gaps between the bars of a Bar Graph, so it doesn’t look like a Histogram.

2When you need to represent trends in time and other variables

Use Line graphs to represent trends in numerous quantities over time, by using multiple lines instead of using bar graphs which will make it more difficult to visualize multiple trends even with stacked or group charts. Line graphs have an advantage in that it’s easier to see small changes on line graphs than bar graphs, and that the line makes the overall trends very clear.

 

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